Sulfurous acid generator

ABSTRACT

A highly efficient apparatus for burning sulfur to sulfur dioxide and generating sulfurous acid comprises a primary sulfur-burning chamber, a sulfur feed tank closely coupled to the primary chamber, a secondary sulfur-burning chamber, and an absorption tower. Air is introduced to the primary chamber under turbulent, high-velocity flow conditions. Gas passes through the secondary chamber under turbulent flow conditions. The apparatus is capable of converting sulfur to sulfur dioxide at a rate in excess of 25 pounds of sulfur per hour per square foot of surface area of the molten pool of sulfur in the primary chamber.

CROSS-REFERENCE

This application is a continuation-in-part of application Ser. No.261,768 filed on May 8, 1981 now abandoned, which is incorporated hereinby this reference.

BACKGROUND

The present invention is directed to an apparatus for burning sulfur tosulfur dioxide, which sulfur dioxide can be used to generate sulfurousacid.

Attention has been directed to treating soil with sulfurous acidintroduced into irrigation water for increasing crop yields. Althoughthis can be accomplished by generating sulfur dioxide at a large centralfacility and transporting the sulfur dioxide to an individual farmer, ithas been found that it is more efficient to generate the sulfur dioxideon site. This technique requires a small, but dependable, sulfur dioxidegenerator. Attempts to produce such a generator are described in U.S.Pat. Nos. 3,226,201; 3,337,989; 3,627,134; 3,907,510 and 4,039,289. Acommercially available sulfur dioxide generator for farmers is availablefrom D & J Harmon Company, Inc., of Bakersfield, Calif. A problem withthese generators is that they are based upon conventional pan-burnertechnology. A limitation of pan burners is that the maximum burning rateis generally about 7 pounds of sulfur per hour per square foot ofburning surface.

It is desirable to have a generator which is more efficient than theconventional pan burner. This would allow the farmer to generatesubstantially more sulfurous acid for treating soil with an apparatus ofsubstantially the same size as prior art equipment.

SUMMARY

The present invention is directed to such a sulfurous acid generator.The apparatus comprises, as its primary components, a primarysulfur-burning chamber, a sulfur feed tank, a secondary sulfur-burningchamber, and an absorption tower. The primary sulfur-burning chambercomprises an enclosure adapted to have a pool of molten sulfur therein,a sulfur inlet at a first lower elevation, an oxygen-containing gasinlet at a second, relatively higher, elevation, and a gas outlet.

Preferably, the sulfur feed tank is closely coupled to the primarychamber to insure that molten sulfur is continuously provided to thesulfur pool. This close coupling can be accomplished with a shortconduit between the sulfur feed tank and the sulfur inlet of the primarychamber, where the conduit has a cross-sectional area of from 15 to 80%of the surface area of the sulfur pool and a length less than thediameter of the pool.

The gas generated in the primary chamber contains sulfur, sulfur dioxideand unreacted oxygen. It is passed to the secondary chamber. Thesecondary chamber provides sufficient residence time and contains meanssuch as baffles which cause the gas passing therethrough to undergoturbulent flow to insure that substantially all of the sulfur isconverted to sulfur dioxide.

The absorption tower has a water inlet at its top and a gas inlet at itsbottom for countercurrent flow of gas and water therein. There is aconduit between the gas inlet of the absorption tower and the outlet ofthe secondary chamber.

Preferably, the oxygen-containing gas inlet is oriented to introduceoxygen-containing gas to the primary chamber tangentially and at a highvelocity of at least about 30 feet per second for forming a turbulent,cyclonic gas flow.

It has been found that the combination of the closely coupled sulfurfeed tank and primary chamber, high velocity tangential introduction ofoxygen-containing gas into the primary chamber, and a secondary chamberresults in burn rates of at least 25 pounds of sulfur per hour persquare foot of burning surface.

In the method of the present invention, a molten pool of sulfur isformed in a primary sulfur-burning chamber, molten sulfur is fed intothe molten pool, and an oxygen-containing gas is introduced into theprimary chamber under high-velocity, turbulent flow conditions forburning sulfur at the surface of the molten pool. This forms an effluentgas stream containing nitrogen, sulfur dioxide, and unreacted sulfur andoxygen. The effluent gas stream is passed to a turbulent-flow, secondarysulfur-burning chamber for combustion of substantially all of the sulfurin the effluent gas to sulfur dioxide. A gas containing sulfur dioxideis withdrawn from the secondary chamber and can be contacted with waterto absorb sulfur dioxide into the water, thereby generating sulfurousacid.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with reference to the followingdescription, appended claims and accompanying drawings, where:

FIG. 1 is a front elevation view of an apparatus for generatingsulfurous acid according to the present invention;

FIG. 2 is a rear elevation view of the apparatus of FIG. 1;

FIG. 3 is a side elevation view of the apparatus of FIG. 1 taken on line3--3 of FIG. 1;

FIG. 4 is a top plan view of the apparatus of FIG. 1;

FIG. 5 is a sectional view of the absorption tower of the apparatus ofFIG. 1 taken on line 5--5 of FIG. 1;

FIG. 6 is a view taken on line 6--6 of FIG. 5; and

FIG. 7 is a top sectional view of the primary sulfur-burning chamber ofthe apparatus of FIG. 1 taken on line 7--7 in FIG. 1.

DESCRIPTION

With reference to the figures, a sulfurous acid generating system 10according to the present invention comprises as its principal elementsan open grid support skid 12, a sulfur feed tank 14, a primarysulfur-burning chamber or zone 16, a secondary sulfur-burning chamber orzone 18, an absorption tower or zone 20, a sulfurous acid receiving tank22, an air blower 24, a pump 26, and a control box 28. All the elementsare supported and mounted on the skid 12 so that the entire unit caneasily be transported such as on a flatbed truck. The elements caneasily be disassembled for transport and replacement, as required.

The sulfur feed tank or hopper 14 is sized to hold in excess of athree-day supply of sulfur, but less than a four-day supply of sulfur.This insures that the owner of the generator 10 needs to check on itsoperation at least twice per week. The feed tank is self-feeding, i.e.,no conveyor or vibrator is required to feed sulfur from the feed tank tothe primary sulfur-burning chamber 16. As shown by FIGS. 1, 2, and 4,the wall of the sulfur feed tank 14 facing the primary sulfur-burningchamber 16 is flat, and the bottom portion of the wall of the sulfurfeed tank 14 farthest from the primary sulfur-burning chamber 16 slopesinwardly toward the primary sulfur-burning chamber. The sulfur feed tankis shown in the figures diametrically opposite the location in which airis introduced into the primary sulfur-burning chamber.

The feed tank 14 has a pivotable top 30 and is made airtight to preventescape of any gases generated in the primary sulfur-burning chamber 16.Also, by making the feed tank 14 airtight, passage of hot gas from theprimary sulfur-burning chamber 16 into the feed tank 14 is minimized.Further, a line 31 extends from the blower discharge to the top of thefeed tank (see FIG. 2) to maintain the pressure in the feed tank higherthan or at least equal to the pressure in the primary chamber. This alsoprevents passage of hot gas into the feed tank 14. Passage of this hotgas is to be avoided to prevent excessive melting of sulfur in the feedtank 14 and to prevent exposure of operating personnel to sulfur dioxidewhen the top 30 is opened.

The primary sulfur-burning chamber 16 comprises a cylindrical enclosure32 formed by a tubular side wall 33, a flat bottom wall 34, and a flattop wall 35. The primary chamber 16 is adapted to have a pool 36 ofmolten sulfur therein. The size of the bottom wall determines thesurface area and diameter of the molten pool 36. As used herein, theterm "burning surface" refers to the top surface of the pool 36. Asulfur inlet 38 is provided in the side wall 33 at a first elevation forfeed of sulfur into the pool 36.

An oxygen-containing gas inlet 40 is provided at a second, relativelyhigher, elevation in the side wall 33 for introduction of anoxygen-containing gas into the enclosure 32. Preferably, the sulfurinlet 38 and the oxygen-containing gas inlet 40 are diametricallyopposite each other. This is done so that incoming cool gas does notcool molten sulfur at the sulfur inlet 38 and so that the hottestportion of the primary chamber is adjacent the feed tank to meltincoming sulfur. It is important that the sulfur at the inlet 38 bemaintained at a temperature higher than its melting point to maintain aconstant feed of molten sulfur to the sulfur pool 36.

An access port 44 in the side wall with a cap 45 gives access to theinside of the primary chamber 16 to light sulfur therein. An electronicignition device 49 having its own port can be used.

A covered cleanup port 46 is provided for cleaning out the primarychamber as necessary.

The gas inlet 40 is oriented to introduce oxygen-containing gastangentially and horizontally, thereby creating a high-velocity,turbulent, cyclonic flow of oxygen-containing gas in the primary chamber16. Contributing to this cyclonic flow of gas is a depending skirt 52that depends to an elevation below the elevation of theoxygen-containing gas inlet. The incoming oxygen containing gas isdisplaced vertically by the skirt 52 before it can exit out the gasoutlet 56. As shown in FIG. 7 the skirt forms a closed-at-its-topannular region 54 proximate to the oxygen-containing gas inlet. Thiscyclonic, turbulent flow of oxygen-containing gas is important in thatit insures that any carbon-containing impurities that collect on the topof the sulfur pool are burnt off. The presence of impurities on the topof the sulfur pool interferes with the burning of the sulfur anddecreases the capacity of the sulfurous acid generator 10.

A gas outlet 56 extends through the top wall 35. This is the only outletfor gas from the primary chamber 16.

A conduit 60 provides molten sulfur to the sulfur pool 36 from the baseof the sulfur feed tank 14 via the sulfur inlet 38 of the primarychamber 16. Sulfur present in the conduit 60 is melted by the heatgenerated by the exothermic combustion of sulfur in the primary chamber16. To maintain a steady flow of sulfur to the primary chamber, it isimportant that the feed tank 14 and the primary chamber 16 be closelycoupled together. This is accomplished by sizing the conduit 60 so itslength is less than the diameter of the burning surface, i.e., is lessthan the diameter of the primary chamber 16. For example, for a primarychamber 16 having a diameter of 15 inches, the maximum length of theconduit 60 (distance A in FIG. 4) preferably is about 10 inches long,i.e., less than about 70% of the diameter of the burning surface pool.Further, the conduit 60 preferably has a large cross-sectional flow areacompared to the diameter of the sulfur pool. Preferably, thecross-sectional area of the conduit 60 is at least about 15%, and morepreferably from 15 to 80%, of the surface area of the burning surface.The cross-sectional area of the conduit 60 can be from about 30 to about40% of the surface area of the pool. For example, for a primary chamberhaving a diameter of 15 inches, a satisfactory conduit is one that is 5inches tall and 15 inches wide, thus providing a cross-sectional area ofabout 40% of the surface area of the sulfur pool.

The secondary chamber 18 has the shape of an elongated box, havingupstanding side walls 62, a first upstanding end wall 63A, secondupstanding end wall 63B, a horizontal top wall 64, and a horizontalbottom wall 65. There is a gas inlet 66 in the bottom wall 65 adjacentthe first end wall 63A and a gas outlet 68 in the bottom wall 65adjacent the second end wall 63B. The gas inlet 66 is located verticallyabove and vertically spaced apart from the gas outlet 56 of the primarychamber 16 and connected thereto by a conduit 70.

The secondary chamber 18 is used for burning any unreacted sulfurpresent in the effluent gas from the primary chamber 16. For thispurpose, it is important that the secondary chamber provides sufficientresidence time for burning of the sulfur and at the same time providesadequate mixing of the gases passing therethrough to bring unoxidizedsulfur into contact with oxygen. To provide adequate residence time inthe secondary chamber, the ratio of the volume of the secondary chamberin cubic feet to the surface area of the sulfur pool in square feet isat least about 1, preferably at least about 1.2, and more preferably atleast about 1.4. The exact ratio depends upon the type and amount ofoxygen-containing gas used to burn the sulfur.

To obtain good mixing of the gases in the secondary chamber, a pluralityof vertical baffles 72 extending alternately up from the bottom wall 65or down from the top wall 64 are provided. Each baffle 72 is welded toboth side walls 62 and either the top wall or the bottom wall and isspaced apart a small distance, in the order of about about 2 to 3inches, from either the opposing top wall 64 or the opposing bottom wall65. This provides a tortuous flow path through the secondary chamber asindicated by arrows 74. Moreover, the relatively small clearance betweenthe baffles 72 and either the top wall 64 or the bottom wall 65 causesgreatly increased gas velocities adjacent the baffle ends, resulting inturbulent flow in the secondary chamber 18 and intimate mixing of thegas passing therethrough. This insures that substantially all of theunreacted sulfur present in the secondary chamber is combined withoxygen to produce sulfur dioxide.

The gas outlet 68 from the secondary chamber 18 is directly above thesulfurous acid receiving tank 22 and is connected thereto by a shortconduit 76 which is provided with a quench water inlet 78. Sulfurousacid 80 is collected in the collection tank 22. There is a gas space 82in the collection tank 22 above the acid 80. Gas from the secondarychamber 18 passes through the conduit 76, through the air space 82, toenter the base of the absorption tower 20.

The absorbtion tower 20 is a packed tower, having near its bottom apacking support grid 84 (see FIG. 3). The tower is substantiallycompletely filled with packing. A suitable packing comprises 1-inchouter diameter, schedule 125 polyvinylchloride pipe cut into 1-inchlengths randomly loaded into the tower.

Alternatively, the packing can be 1 inch polypropylene saddles in adepth of 5 feet, 3 inches on top of six inches of 1 inch stainles steelpall rings to dissipate the heat.

The tower has a covered access port 85.

With reference to FIGS. 5 and 6, the top of tower 20 is provided with ademister 87 that is supported by four brackets 88 welded to the insidewall of the tower 20. The demister 87 separates any entering liquid fromvapor passing out of the top of the absorption tower. A suitabledemister is available from Otto H. York Company.

The brackets 88 also support a water distribution assembly 90 thatcomprises a horizontal plate 92 attached to the underside of thebrackets 88. In the center of the plate 92 is a hole 94 in which ismounted an upstanding female threaded section of pipe 96 adapted toreceive male threaded plastic pipe 98 which supplies water to the tower20.

Depending from the plate 92 below the hole 94 supported by threevertical hanger straps 102 is a flat, horizontal perforated plate 104.Surrounding the straps 102 and plate 104 is a cylindrical distributionpipe 108 open at its bottom and attached at its top to the plate 92. Thedistribution pipe has a plurality of perforations 110, through which thebulk of the water passes. The water distribution assembly 90 insuressubstantially uniform flow of water through the absorption tower 20.

Altenratively, a spray nozzle available from Spraying Systems ofWheaton, Ill., model 2RR 9545, can be used.

Water for the quench water and for the absorption tower 20 is providedby an inlet pipe 112 that is connected to a T-connector 114. TheT-connector distributes water through a valve 116 to a hose 118connected to the quench water inlet 78. The other side of theT-connector is connected to a valve 120 that is used to control flow ofwater through a PVC pipe 122 that is connected to the segment of plasticpipe 98 coupled to the water distribution assembly 90.

In a preferred version of the absorption tower, the tower is made ofplastic, such as PVC, rather than stainless steel, and the gas inlet isa nozzle that extends into the tower and directs incoming gas downwardtoward the receiving tank 22. With this configuration, incoming watercools the gas inlet nozzle and helps avoid corrosion. This configurationis not our invention but was disclosed to us in secrecy and confidenceand is the invention of William E. Sells, Jr.

The oxygen-containing gas can be any gas that provides free oxygen forcombining with sulfur. Preferably, the gas is air, although air enrichedwith oxygen, or air of reduced oxygen content can be used. The blower 24supplies the air through a conduit 124 that is connected to theoxygen-containing gas inlet 40 of the primary sulfur-burning chamber 16.A valve 126 is provided in the conduit 124 to control the rate at whichoxygen-containing gas is provided to the primary sulfur-burning chamber.

The sulfurous acid removal system comprises the discharge pump 26 thatis connected by a hose 128 to the bottom of the sulfurous acid receivingtank 22. There is a valved discharge line 130 from the pump 26. A levelcontrol system (not shown) is used to insure that the pump 26 does notwithdraw sulfurous acid from the receiving tank 22 at a rate faster thanit is generated.

A standpipe 122 is connected to the base of the receiving tank 22 toinsure that the absorption tower 20 does not become flooded with liquid.The standpipe 122 can be pivoted to drain the receiving tank 22 duringshut-down.

Carbon steel can be used for construction of the sulfurous acidgenerator 10, although preferably stainless steel is used for componentsin contact with sulfur dioxide and high heat such as the feed tank,conduits 60, 70 and 76, and the primary and secondary combustionchambers.

The control box 30 is provided with electrical controls for operatingthe discharge pump 26 and the blower 24. In addition, sensing elements(not shown) are provided to monitor the temperature in the absorptiontower, the water pressure of incoming water, and the pH of the sulfurousacid. If the pressure of incoming water is below a set value or if thetemperature in the absorption tower becomes too high, the flow ofoxygen-containing gas is shut off by shutting down the blower 24.

In operation of the generator 10, sulfur in the primary sulfur-burningchamber 16 is ignited and air is continuously blown into chamber by theblower 24 via the line 124 and the oxygen-containing gas inlet 40. Theamount of the air introduced controls the rate of which sulfur is burnedup to the maximum capacity of the apparatus 10. At maximum capacity, inthe order of about 25 to about 30 pounds of sulfur per square foot ofburning surface per hour is burned. About 1 to about 2 CFM (cubic feetper minute) of air per pound of sulfur burned is used.

Thus air is introduced into the primary burner at a rate of at least 25CFM, and preferably from about 25 to about 60 CFM per square foot ofburning surface. At rates higher than about 60 to 65 CFM the flame canbe blown out.

The oxygen-containing gas inlet 40 is sized so that theoxygen-containing gas enters the primary chamber at high velocity,preferably at least about 30 feet per second. Preferably, the velocityis less than about 125 feet per second to avoid blowing out the flame.

An advantage of these high velocities is that high sulfur burning ratesare achieved because of burn off of carsul. Carsul is asulfur/cabonaceous material resulting from sulfur combining withcarbonaceous materials. Carsul can collect on the surface of the sulfurpool, preventing oxygen from reaching the underlying sulfur, and therebyreducing sulfur burning rates. Because of the use of high air rates thecarsul accummulates at the center of the pool where portions rise abovethe level of the liquid sulfur. This carsul is no longer coated withsulfur, and thus can burn off.

The velocity at which air is introduced into the primary chamber isdetermined by dividing the rate at which air is introduced (cfm) by thenozzle diameter (sq.ft.).

Preferably, the temperature in the primary chamber is sufficiently highthat sulfur in the pool is vaporized. A portion of this vaporized sulfuris burned in the primary chamber in the gas space above the sulfur pool.Effluent gas passes from the primary sulfur-burning chamber 16 via theconduit 70 into the secondary sulfur-burning chamber 18. The effluentgas contains sulfur dioxide, carbon dioxide, oxygen, and unreactedsulfur vapor. In the secondary chamber 18, because of the turbulent flowconditions and long retention time, substantially all of the sulfur inthe effluent gas is converted to sulfur dioxide.

The maximum temperature in the secondary burning chamber occurs in thefirst section 134 that is formed by the first side wall 63A, the topwall 64, the bottom wall 65 and the first baffle 72A. The maximumtemperature is at least about 1000° F., and preferably is maintainedbetween about 1000 to 1500 degrees F., and more preferably between about1300 and 1400 degrees F. When the temperature in the secondary chamberis mentioned herein, reference is being made to the temperature in thefirst section of the secondary chamber.

The velocity of the inlet gas in the secondary sulfur-burning chamber isat its maximum proximate to the end of the baffles. This velocitypreferably is at least about 750 feet per minute to obtain turbulencewith resultant oxidation of substantially all of the sulfur present.

Gas passing from the secondary chamber is quenched with quench waterintroduced through the quench water inlet 78 at a rate of about 0.1 toabout 0.15 gallons per minute of water per pound per hour of sulfurburned to prevent damage to the packing in the absorption tower. Therate is varied depending upon the temperature in the secondary chamber18.

Some sulfur dioxide in the gas withdrawn from the secondary chamber isabsorbed in the quench water which is collected in the receiving tank22. The remainder of the sulfur dioxide is absorbed into waterintroduced into the top of the absorbtion tower 12 through thedistribution assembly 90 as the gas passes upwardly through the tower.Water in the tower is used at a rate of from about 1 to about 2 gallonsper minute per pound of sulfur burned per hour.

The sulfur dioxide content of the gas withdrawn from the secondarysulfur-burning chamber 18, prior to the quench, is about 8% to 14%sulfur dioxide by volume, while the gas passing out of the absorbtiontower contains substantially no sulfur dioxide.

Because of the blower 24, the entire system, including the primary andsecondary chambers, is under positive pressure.

The apparatus and process of the present invention achieve remarkablyhigh rates of conversion of sulfur to sulfurous acid for the size of theequipment. Sulfur burn rates up to about 30 pounds per hour per squarefoot of burning surface area have been achieved. Although not bound bytheory, it is believed that this is a result of at least three featuresof the present invention. The first feature is the close coupling of thefeed tank 14 with the primary chamber 16, insuring that an adequatesupply of molten sulfur is provided to the sulfur pool.

The second feature is the cyclonic, high-velocity gas flow in theprimary chamber. This insures that carbon-containing impurities on thesurface of the sulfur pool are burned off and that a high proportion ofthe oxygen introduced into the primary chamber reacts with sulfur.Further, a cyclonic cone is formed, within which vaporized sulfur isoxidized to sulfur dioxide.

The third feature is the use of the secondary sulfur-burning chamber toconvert sulfur to sulfur dioxide. Thus, not all the burning is requiredto occur near the surface of the sulfur pool. The long residence timeand tortuous, turbulent flow in the secondary sulfur-burning chamberinsure conversion of the sulfur to sulfur dioxide.

A further advantage of the present invention is that it is a compactunit and can fit on a single skid for easy transportation to the field.Moreover, flanges can be included in critical places such as on theconduits to and from the secondary sulfur-burning chamber so thatportions of the apparatus especially prone to corrosion can easily bereplaced and the generator 10 can be disassembled for transport.

EXAMPLE

An apparatus according to the present invention has a primarysulfur-burning chamber with a diameter of 151/2 inches (sulfur surfacearea of 1.27 square feet) and an oxygen-containing gas inlet nozzle of 2inches. The conduit 60 from the feed tank 14 was 10 inches long, 5inches tall, and 151/2 inches wide. Sulfur was burned at the rate of 35pounds per hour with ambient-temperature air introduced at the rate of65 CFM. Ambient-temperature quench water was provided at the rate ofabout 5 gallons per minute, and ambient-temperature water was introducedto the top of the absorbtion tower at a rate of about 50 gallons perminute. The secondary sulfur-burning chamber was 2 feet 8 inches long, 1foot 5 inches tall, and 6 inches wide. The baffles were spaced apart 2inches from the opposing top or bottom wall, providing a 2-inchclearance for passage of gas through the chamber. The temperature in thefirst section 134 of the secondary sulfur-burning chamber was about 1350degrees F.

The top of the absorbtion tower was about 6 feet 8 inches from the topof the skid, and the top of the collection tank was 1 foot 8 inches fromthe top of the skid. The diameter of the absorbtion tower was about 15inches.

Although the present invention has been described in considerable detailwith reference to certain preferred versions thereof, other versions arepossible. For example, the elongated secondary chamber can be verticallyoriented rather than horizontally oriented. In addition, the absorptiontower and quench do not have to be part of the system. The sulfurdioxide generated in the primary and secondary sulfur-burning chamberscan be used without dissolving it in water.

Furthermore, the spatial orientation of the elements of the sulfurousacid-generating system 10 can be changed. Therefore, the spirit andscope of the appended claims should not necessarily be limited to thedescription of the preferred versions contained herein.

What is claimed is:
 1. Apparatus for burning sulfur with oxygencontained in air comprising:(a) a primary sulfur-burning chambercomprising (1) an enclosure adapted to have a pool of molten sulfurtherein, (2) a sulfur inlet at a first, lower elevation of the enclosurefor feed of sulfur into such a pool, (3) an air inlet at a second,relatively higher elevation of the enclosure above the sulfur inlet forintroduction of air tangentially into the primary sulfur-burningchamber, and (4) a gas outlet from the enclosure; (b) a sulfur feed tankfor supplying sulfur to the pool of molten sulfur in the primarychamber, the sulfur feed tank being adapted to receive heat from theprimary sulfur-burning chamber for the melting of sulfur in the sulfurfeed tank; (c) a conduit from the sulfur feed tank to the sulfur inletfor transferring sulfur from the sulfur feed tank to the primaysulfur-burning chamber, the cross-sectional area of the conduit being atleast 30% of the surface area of the pool; (d) means for introducingsubstantially all of the air used for burning the sulfur to the airinlet for burning and vaporizing the sulfur supplied to the pool to forman effluent gas containing sulfur, sulfur dioxide, and oxygen; and (e) asecondary sulfur-burning chamber having an inlet at a first end thereofand an outlet at a second end thereof, the secondary chamber receivingat its inlet effluent gas containing sulfur, sulfur dioxide, and oxygendischarged from the gas outlet of the primary chamber, the secondarychamber having a tortuous flow path for causing turbulent flow of gaspassing therethrough for combustion of substantially all of the sulfurin the effluent gas to sulfur dioxide.
 2. The apparatus of claim 1 inwhich the pool is circular.
 3. The apparatus of claim 2 in which theprimary chamber comprises an internal skirt, the skirt forming aclosed-at-its-top annular region above the air inlet.
 4. The apparatusof claim 3 in which the air inlet is substantially diametricallyopposite the sulfur feed tank.
 5. The apparatus of claim 1 or 4 in whichthe sulfur inlet and the air inlet are substantially diametericallyopposed.
 6. The apparatus of claim 1 or 2 in which the conduitcross-sectional area is up to about 40% of the surface area of the pool.7. Apparatus for generating sulfurous acid comprising:(a) a primarysulfur-burning chamber comprising (1) an enclosure adapted to have acircular pool of molten sulfur therein, (2) a sulfur inlet at a first,lower elevation of the enclosure for feed of sulfur into such a pool,(3) an air inlet at a second, relatively higher elevation of theenclosure above the sulfur inlet and substantially diametricallyopposite the sulfur inlet, (4) a gas outlet in the top of the enclosure,and (5) an internal skirt for forming a closed-at-its-top annular regionabove the air inlet; (b) a sulfur feed tank closely coupled to theprimary sulfur-burning chamber for supplying sulfur to the pool ofmolten sulfur in the primary chamber at a rate of at least about 25pounds per hour per square foot of the surface area of the pool, thesulfur feed tank being substantially diametrically opposite the airinlet, the wall of the sulfur feed tank facing the primarysulfur-burning chamber being flat for receiving heat from the primarysulfur burning chamber for melting of sulfur in the sulfur feed tank,and the bottom portion of the wall of the sulfur feed tank farthest fromthe primary sulfur chamber sloping inwardly toward the primarysulfur-burning chamber; (c) a first conduit from the sulfur feed tank tothe sulfur inlet of the primary sulfur-burning chamber, thecross-sectional area of the first conduit being about 40% of the surfacearea of the pool and the length of the first conduit being less than thediameter of the pool; (d) means for introducing substantially all of theair used for burning the sulfur to the air inlet at a rate of at leastabout 25 CFM per square foot of the pool of molten sulfur and a velocityof at least about 30 feet per second and less than a rate and a velocitythat blows out a flame for burning and vaporizing the sulfur supplied tothe pool to form an effluent gas containing sulfur, sulfur dioxide, andoxygen, wherein the air inlet comprises a nozzle oriented to introduceair to the annular regional tangentially and horizontally; (e) anelongated, horizontally oriented secondary sulfur-burning chamber havingan inlet at a first end thereof and an outlet at the opposite endthereof, the secondary chamber receiving at its inlet effluent gascontaining sulfur, sulfur dioxide, and oxygen discharged from the gasoutlet of the primary chamber, the secondary chamber containing aplurality of baffles extending across the flow path through thesecondary chamber creating a tortuous path for flow of gas passingthrough the secondary chamber for combustion of substantially all of thesulfur in the effluent gas to sulfur dioxide; (f) a sulfur dioxideabsorption tower having a water inlet at the top thereof and a gas inletat the bottom thereof for countercurrent flow of gas and water therein;(g) a second conduit between the gas inlet of the absorption tower andthe outlet of the secondary sulfur-burning chamber; and (h) means forintroducing water to the absorption tower at the water inlet.
 8. Theapparatus of claim 1 or 7 including means for maintaining the pressureat the top of the feed tank no less than the pressure in the primarychamber.
 9. The apparatus of claim 1 wherein the sulfur feed tank isclosely coupled to the primary chamber, the length of the conduit beingless than the equivalent diameter of the pool.
 10. The apparatus ofclaim 1 in which the width of the conduit is about equal to theequivalent diameter of the pool.
 11. The apparatus of claim 1 in whichthe conduit cross-sectional area is about 40% of the surface area of thepool.
 12. The apparatus of claim 1 in which the air inlet introduces airhorizontally.
 13. The apparatus of claim 1 in which the secondarychamber contains a plurality of baffles and wherein the flow pathincludes portions of reduced cross-sectional area at the ends of thebaffles.
 14. The apparatus of claim 1 in which the sulfur feed tank hasa flat wall facing the primary sulfur-burning chamber.
 15. The apparatusof claim 1 or 14 in which the bottom portion of the wall of the sulfurfeed tank farthest from the primary sulfur-burning chamber is flat andslopes inwardly toward the primary sulfur-burning chamber.
 16. Anapparatus for burning sulfur with oxygen contained in air comprising:(a)a primary sulfur-burning chamber comprising (1) an enclosure adapted tohave a pool of molten sulfur therein, the pool having a surface area,(2) a sulfur inlet at a first, lower elevation of the enclosure for feedof sulfur into such a pool, (3) an air inlet at a second, relativelyhigher elevation of the enclosure above the sulfur inlet for introducingair tangentially into the primary sulfur burning chamber, the air inletbeing diametrically opposite the sulfur inlet, and (4) a gas outlet fromthe enclosure; (b) a sulfur feed tank for supplying sulfur to the poolof sulfur in the primary chamber, the sulfur feed tank having a flatwall facing the primary sulfur-burning chamber for receiving heat fromthe primary sulfur-burning chamber for melting of sulfur in the sulfurfeed tank, and wherein the bottom portion of the wall of the sulfur feedtank farthest from the primary sulfur-burning chamber is flat and slopesinwardly toward the primary sulfur-burning chamber, the sulfur feed tankbeing substantially diametrically opposite the air inlet; (c) a conduitfrom the sulfur feed tank to the sulfur inlet for transferring sulfurfrom the sulfur feed tank to the primary sulfur-burning chamber, thecross-sectional area of the conduit being at least 30% of the surfacearea of the pool; (d) means for introducing air used for burning thesulfur to the air inlet for burning and vaporizing the sulfur suppliedto the pool to form an effluent gas containing sulfur, sulfur dioxide,and oxygen; and (e) a tortuous flow path secondary sulfur-burningchamber having an inlet at a first end thereof and an outlet at a secondend thereof, the secondary chamber receiving at its inlet effluent gascontaining sulfur, sulfur dioxide and oxygen discharged from the gasoutlet of the primary chamber, substantially all of the sulfur in theeffluent gas being combusted to sulfur dioxide in the secondary chamber.17. A continuous process for producing sulfur dioxide by burning sulfurwith oxygen contained in air comprising the steps of:(a) melting sulfurin a sulfur melting zone; (b) feeding molten sulfur from the sulfurmelting zone into a molten pool of sulfur in a primary sulfur-burningzone at a rate of at least 25 pounds of sulfur per hour per square footof surface area of the pool, the sulfur being fed to the pool through aconduit, the cross-sectional area of the conduit being at least 30% ofthe surface area of the pool; (c) introducing substantially all of theair used for burning the sulfur into the primary zone tangentially underturbulent flow conditions (i) for burning sulfur at the surface of themolten pool with a flame being present, (ii) for vaporizing sulfur fromthe pool to form an effluent gas stream containing sulfur, sulfurdioxide, and unreacted oxygen, and (iii) for melting sulfur in thesulfur melting zone, the air being introduced at a rate sufficientlyhigh for burning and vaporizing the sulfur fed to the pool and at a ratesufficiently low as to not blow out the flame; (d) passing the effluentgas stream to a turbulent flow, tortuous flow path secondarysulfur-burning zone for combustion of substantially all of the sulfur inthe effluent gas to sulfur dioxide, the effluent gas stream undergoingturbulent flow in the secondary zone; and (e) withdrawing gas containingsulfur dioxide from the secondary zone; wherein substantially all of theheat for melting sulfur in the melting zone is from burning sulfur inthe primary and secondary sulfur-burning zone.
 18. The process of claim17 in which the secondary sulfur-burning zone is maintained at atemperature of at least about 1000° F.
 19. The process of claim 17 inwhich the secondary sulfur-burning zone is maintained at a temperatureof from about 1000° to about 1500° F.
 20. The process of claim 17 inwhich air is introduced into the primary zone at a velocity of less thanabout 125 feet per second.
 21. The process of claim 17 in which air isintroduced into the primary zone at a rate of less than about 60 CFM persquare foot of the pool of molten sulfur.
 22. The process of claim 17 inwhich the pool is circular.
 23. The process of claim 17 or 22 in whichthe conduit cross-sectional area is about 40% of the surface area of thepool.
 24. The process of claim 17 or 22 in which the width of theconduit is about equal to the equivalent diameter of the pool.
 25. Theprocess of claim 17 in which the sulfur feed tank has a flat wall facingthe primary sulfur-burning zone.
 26. The process of claim 17 or 25 inwhich the bottom portion of the wall of the sulfur feed tank farthestfrom the primary sulfur-burning zone is flat and slopes inwardly towardthe primary sulfur-burning zone.
 27. The process of claim 17 in whichthe air is introduced into the primary zone at a location diametricallyopposite the location in which the molten sulfur is introduced into theprimary zone.
 28. The process of claim 17 or 27 in which the air isintroduced into the primary zone at a location diametrically oppositethe sulfur melting zone.
 29. A continuous process for producingsulfurous acid by burning sulfur with oxygen contained in air comprisingthe steps of;(a) melting sulfur in a sulfur melting zone; (b) feedingmolten sulfur from the sulfur melting zone into a pool of sulfur in aprimary sulfur burning zone at a rate of at least 25 pounds of sulfurper hour per square foot of surface area of the pool, the sulfur beingfed to the pool through a conduit, the cross-sectional area of theconduit being about 40% of the surface area of the pool, the length ofthe conduit being less than the diameter of the pool, and the width ofthe conduit being about equal to the diameter of the pool, the sulfurmelting zone having a flat wall facing the primary sulfur-burning zone,the bottom portion of the wall of the melting zone farthest from theprimary sulfur-burning zone sloping inwardly toward the primarysulfur-burning zone; (c) introducing substantially all of the air usedfor burning the sulfur into the primary zone under turbulent flowconditions for (i) burning sulfur at the surface of the molten pool witha flame being present, (ii) for vaporizing sulfur from the pool to forman effluent gas stream containing sulfur, sulfur dioxide, and unreactedoxygen, and (iii) for heating sulfur in the sulfur melting zone, the airbeing introduced at a rate of from about 25 to about 60 CFM per squarefoot of the pool of molten sulfur, the air being introduced at alocation substantially diametrically opposite the location sulfur is fedinto the primary sulfur-burning zone and substantially diametricallyopposite the sulfur melting zone; (d) passing the effluent gas stream toa turbulent-flow, tortuous flow path, secondary sulfur-burning zone forcombustion of substantially all of the sulfur in the effluent gas tosulfur dioxide at a temperature of from about 1000° to about 1500° F.,the effluent gas stream undergoing turbulent flow in the secondary zone;and (e) withdrawing gas containing sulfur dioxide from the secondaryzone and contacting the withdrawn gas with water to absorb sulfurdioxide into the water; wherein substantially all of the heat formelting the sulfur in the sulfur melting zone is from burning sulfur inthe primary and secondary sulfur-burning zones.
 30. A continuous processfor producing sulfur dioxide by burning sulfur with oxygen contained inair comprising the steps of:(a) melting sulfur in a sulfur melting zone;(b) feeding molten sulfur from the sulfur melting zone into a moltenpool of sulfur in a primary sulfur-burning zone at a rate of at least 25pounds of sulfur per hour per square foot of surface area of the pool,the sulfur being fed to the pool through a conduit, the cross-sectionalarea of the conduit being at least 30% of the surface area of the pool,the wall of the sulfur feed tank facing the primary sulfur-burning zonebeing flat and the bottom portion of the wall of the sulfur feed tankfarthest from the primary sulfur-burning zone being flat and slopinginwardly toward the primary sulfur-burning zone; (c) introducingsubstantially all of the air used for burning the sulfur into theprimary zone tangentially under turbulent flow conditions (i) forburning the sulfur at the surface of the molten pool with a flame beingpresent, (ii) for vaporizing sulfur from the pool to form an effluentgas stream containing sulfur, sulfur dioxide, and unreacted oxygen, and(iii) for melting sulfur in the sulfur melting zone, the air beingintroduced at a rate sufficiently high for burning and vaporizing thesulfur fed to the pool and at a rate sufficiently low as to not blow outthe flame, the air being introduced at a location substantiallydiametrically opposite the location sulfur is fed into the molten pooland substantially diametrically opposite the sulfur melting zone; (d)passing the effluent gas stream to a tortuous flow path secondarysulfur-burning zone for combustion of substantially all of the sulfur inthe effluent gas to sulfur dioxide; and (e) withdrawing gas containingsulfur-dioxide from the secondary zone; wherein substantially all of theheat for melting the sulfur is from burning sulfur in the primary andsecondary sulfur-burning zones.